Research On The Thermal Fatigue Property Of The Aluminum Ingot Mould Material For Continuous Casting Machine Application

Thermal fatigue is one of the main failure patterns for the Al-casting mould and an important factor to limit the life of Al-casting mould.Thus it is very important to improving thermal fatigue resistance of the Aluminum Ingot Mould Material apply for Continuous casting Machine,in order to raise the life of Mould and widen the application of the Aluminum Ingot Continuous casting Machine in domestic.This paper has made a study by laboratory simulation method on thermal fatigue property of aluminum ingot mould material,which has served as Al-continuous casting machine.The thermal fatigue properties of the mould with different chemical compositions under different heat treatment process conditions were studied.The thermal characteristic of the ductile cast iron and the initiation and propagation mechanism of thermal fatigue cracks were also investigated.All of these provide a theoretical basis for improve the resistance to thermal fatigue properties of Aluminum ingot mould.The results show that:The thermal fatigue micro-cracks of the ductile iron initiate at the boundary between graphite and matrix,because the low intensity of the graphite branch is easier cause stress concentration then due to the crack initiation.Micro-cracks expand generally along the nearest path of spheroidal graphite.In the primary period of thermal fatigue crack propagation,the average crack length can be used as the criterion of the thermal fatigue damage degree,but the extension of the crack width gradually occupy the leading position in delayed crazing period,so we defined new criterion the surface crack damage characteristic factor D(D=A%·W/L) for lend support to judge the criterion of the thermal fatigue damage degree.By study of the fatigue crack propagation,we found that the thermal fatigue damage degree can be represented by the surface crack damage characteristic factor D.The comparing experiments show that:the thermal fatigue property of the ductile cast iron mould is markedly influenced by heat treatment process.Through selecting the proper heat treatment process we can improve the thermal fatigue resistance of the ductile cast iron obviously.According to contrast and analysis the heat treatment processes and thermal fatigue experiments,we selected heat treatment parameters that have best mechanical property and thermal-resistant property,the parameters are:annealing temperature is 900℃,holding time is 2 hours and normalization temperature is 900℃,holding time is 2 hours;annealing temperature is 900℃,holding time is 2 hours and austempering temperature is 300℃,holding time is 1 hour.The experiment results show that after the annealing add normalizing heat treatment process for ductile cast iron,the phase composition had been optimized and could make it have better matrix organization and mechanical property cause plenty of tiny perlitic and a small quantity of ferritic matrix structure had been formatted;Then through the annealing add isothermal quenching heat treatment process for ductile cast iron,plenty of lower bainite needle organization had been made up in matrix organization and made it also have high mechanical intensity and suitable toughness.In general,through those two kind of heat treatment process,the mechanical capability and the heat-fatigue resistance performance of ductile cast iron had been further improved then extend aluminum ingots casting machine mould utility longevity.